Various desalination or demineralization or crystallization processes are currently known. The main processes will be restated hereinbelow with the disadvantages which are associated with them:
the precipitation of salts of very slight solubility which are separated from the treated water by settling or filtration. Thus, French Patent FR-A-2,339,575 discloses a process and a plant for the treatment of water by crystalline precipitation and settling which consists in producing a homogeneous dispersion of water to be treated, of reagents necessary for the crystalline precipitation and of sludges separated from the water to be treated and in settling this dispersion, the crystalline precipitation reaction being completed during the settling. The disadvantage of this known technique lies in the use of reagents which can be very expensive for the purpose of reducing their contents of salts of very slight solubility below their solubility; PA1 percolation through a bed of ion-exchange resins which makes it possible to replace all or part of the ions by other ions. This solution exhibits the disadvantage of high consumption of chemical reagents and that of the production of saline, indeed highly saline, regeneration eluates; PA1 filtration through reverse osmosis or nanofiltration membranes which are selective with respect to certain salts and which concentrate them in a fraction of the treated flow. The disadvantage of this technique lies in the production of a filtration concentrate which represents a significant fraction of the flow of the water to be treated (of the order of 10 to 70%, depending on the initial salinity and the degree of conversion adopted); PA1 evaporation, which produces demineralized water by condensation of the vapor produced and which concentrates the salinity into a brine. This solution leads to very high energy consumption and the production of a saline brine which has to be either discharged or crystallized, the latter stage resulting in a very high investment cost; PA1 electrodialysis, involving ion-exchange membranes which make it possible to extract the inorganic salts from the solutions and to concentrate them into a brine, the purified water flow being separated from the brine flow by the said ion-exchange membranes. PA1 a) conditioning the solutions, clarified before-hand, using a chemical reagent which is an inhibitor of the precipitation of salts, optionally followed by a filtration; PA1 b) concentrating the salts into a supersaturated brine representing a fraction of the flow of between 5 and 80% of the flow of the solution to be treated; PA1 c) in this brine, reducing, indeed removing, the effect of the precipitation inhibitor and precipitating the crystallizable supersaturated salts in the concentrated fraction.